Solid oxide fuel cell system with carbon capture and improved efficiency

Abstract

A fuel cell system includes a fuel cell module having an inlet and an outlet. The fuel cell module receives a fuel stream including a gaseous fuel and expels a spent fuel stream. The system also includes an exhaust treatment module disposed relative to the fuel cell module such that waste heat from the fuel cell module is available for use by the exhaust treatment module. The system is configured to direct a first portion of the spent fuel stream to the exhaust treatment module, where the spent fuel stream includes spent fuel and at least one gaseous byproduct including oxygen and carbon dioxide. The exhaust treatment module uses the waste heat from the fuel cell module to subject the first portion of the spent fuel stream to co-electrolysis to produce a fuel-rich stream. The system is configured to direct the fuel-rich stream to the inlet of the fuel cell module.

Description

[0001] Cross-reference of related applications

[0002] This application claims the benefit and priority of U.S. Provisional Application No. 63 / 199060, filed on December 4, 2020, which is incorporated herein by reference in its entirety. Background Technology

[0003] This application relates generally to the field of solid oxide fuel cell (SOFC) systems, and more specifically to SOFC systems with high-purity carbon dioxide (CO2) exhaust streams to facilitate carbon capture.

[0004] Typically, a fuel cell comprises an anode, a cathode, and an electrolyte layer that work together to drive a chemical reaction to generate electricity. Specifically, a SOFC is a solid-state electrochemical cell comprising a solid, impermeable electrolyte sandwiched between a porous anode and a porous cathode. Oxygen is transported through the cathode to the cathode / electrolyte interface, where it is reduced to oxygen ions, which then migrate through the electrolyte to the anode. At the anode, the oxygen ions react with a fuel such as hydrogen or methane, releasing electrons. These electrons travel through an external circuit back to the cathode to generate electricity.

[0005] Anode exhaust gas can contain a mixture of steam, hydrogen, carbon monoxide, and carbon dioxide, producing the anode exhaust gas as a byproduct of the fuel cell anode. The anode exhaust gas contains useful byproduct gases such as hydrogen and carbon monoxide, which can be output as syngas for other uses, such as fuel for fuel cells or feedstock for other chemical reactions. Furthermore, the CO2 and water in the exhaust gas can also be output for isolation or other downstream treatment. However, to prepare anode exhaust gas suitable for such applications, the CO2 present in the anode exhaust gas must be separated from the remaining byproduct gases.

[0006] Therefore, it would be advantageous to provide an SOFC system that delivers a CO2-rich exhaust stream to enable easy carbon capture without compromising system efficiency or causing excessive operating costs. Summary of the Invention

[0007] One aspect of this disclosure relates to a fuel cell system. The system includes a fuel cell module having an inlet and an outlet, the fuel cell module being configured to receive a fuel stream comprising gaseous fuel at the inlet and discharge a consumed fuel stream from the outlet. The system further includes an exhaust treatment module in fluid communication with the fuel cell module. The exhaust treatment module is positioned relative to the fuel cell module such that waste heat energy from the fuel cell module is utilized by the exhaust treatment module. The system is configured to direct a first portion of the consumed fuel stream to the exhaust treatment module, wherein the consumed fuel stream comprises consumed fuel and at least one gaseous byproduct comprising oxygen and carbon dioxide. The exhaust treatment module is configured to use the waste heat from the fuel cell module to co-electrolyze the first portion of the consumed fuel stream to produce a fuel-rich feed stream. The system is configured to direct the fuel-rich feed stream to the inlet of the fuel cell module.

[0008] In various embodiments, the system further includes a controller configured to operate at least one of the fuel cell module or the exhaust treatment module based on the composition of the consumed fuel stream. In some embodiments, the fuel cell module includes at least one solid oxide fuel cell. In other embodiments, the exhaust treatment module includes at least one solid oxide electrolysis stack. In still other embodiments, the exhaust treatment module is housed within the fuel cell module. In various embodiments, the fuel cell module includes a plurality of fuel cell stacks, wherein a first subset of the plurality of fuel cell stacks is a solid oxide fuel cell, and wherein a second subset of the plurality of fuel cell stacks is a solid oxide electrolysis stack. In some embodiments, the exhaust treatment module is separate from the fuel cell module. In other embodiments, the exhaust treatment module includes a plurality of branches electrically connected in parallel, each of the plurality of branches having at least one solid oxide electrolysis stack, and each solid oxide electrolysis stack including a plurality of solid oxide electrolysis cells.

[0009] In various embodiments, the system further includes an afterburner in fluid communication with the fuel cell module and disposed downstream of the outlet. In some embodiments, the afterburner is configured to receive a second portion of the consumed fuel stream and generate a first exhaust stream by reacting unreacted fuel within the second portion. In other embodiments, the exhaust treatment module is configured to discharge oxygen generated during co-electrolysis of the first portion in the outlet stream. In still other embodiments, the system is configured to direct the outlet stream to the afterburner, wherein oxygen from the first outlet stream promotes combustion of the unreacted fuel contained in the first portion. In various embodiments, the afterburner is configured to discharge a second exhaust stream consisting of carbon dioxide. In some embodiments, the exhaust treatment module is configured to provide a reducing gas to the fuel cell module. In other embodiments, the exhaust treatment module is configured to provide the reducing gas during a shutdown event of the fuel cell system.

[0010] Another aspect of this disclosure relates to a method of operating a fuel cell system. The method includes discharging a consumed fuel stream from an outlet by a fuel cell module configured to receive gaseous fuel at an inlet. The method further includes receiving a first portion of the consumed fuel stream by an exhaust treatment module, the first portion comprising consumed fuel and at least one gaseous byproduct comprising carbon dioxide and oxygen. The method also includes generating a fuel-rich stream from the first portion by the exhaust treatment module through co-electrolysis using waste heat from the fuel cell module. The method further includes directing the fuel-rich stream generated by the exhaust treatment module back to the fuel cell module by the fuel cell system.

[0011] In some embodiments, the method further includes receiving a second portion of the consumed fuel stream by an afterburner in fluid communication with the fuel cell module; and generating a first exhaust stream by the afterburner by reacting unreacted fuel within the second portion. In various embodiments, the method further includes removing water from at least a portion of the fuel-rich stream by a water separation unit in fluid communication with the exhaust treatment module. In other embodiments, the method further includes operating at least one of the fuel cell module or the exhaust treatment module by a controller in communication with the fuel cell system based on the composition of the consumed fuel stream. In yet another embodiment, the controller is configured to adjust at least one operating condition of the fuel cell system based on the composition of gaseous fuel within the fuel cell system. Attached Figure Description

[0012] The advantages and features constituting this disclosure, as well as the clear concept of the construction and operation of typical mechanisms provided by this disclosure, will become more apparent from the exemplary and therefore non-limiting embodiments shown in the accompanying drawings, which form part of this specification, wherein like reference numerals denote like elements in multiple views, and in the drawings:

[0013] Figure 1 This is a schematic representation of a fuel cell system according to an exemplary embodiment.

[0014] Figure 2 This is a schematic representation of a fuel cell system including an exhaust gas treatment module for carbon capture, according to an exemplary embodiment.

[0015] Figure 3 This is a schematic representation of a fuel cell system according to another exemplary embodiment.

[0016] Figure 4 This is a schematic representation of a fuel cell system including an exhaust gas treatment module for carbon capture, according to another exemplary embodiment.

[0017] The foregoing and other features of this disclosure will become apparent from the following description and the appended claims in conjunction with the accompanying drawings. It should be understood that these drawings depict only a few embodiments according to this disclosure and are therefore not intended to limit the scope of the disclosure, which will be described with additional features and details using the drawings. Detailed Implementation

[0018] In the following detailed description, reference is made to the accompanying drawings, which form part of the detailed description. In the drawings, similar symbols generally identify similar parts unless the context otherwise requires. The illustrative embodiments described in the detailed description, drawings, and claims are not intended to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that, as generally described herein and illustrated in the drawings, aspects of this disclosure can be arranged, substituted, combined, and designed in a variety of different configurations, all of which are expressly contemplated and form part of this disclosure.

[0019] This disclosure provides a fuel cell system capable of efficient CO2 processing and subsequent carbon capture without loss of efficiency. Furthermore, the fuel cell system of the present invention includes an exhaust gas treatment module that not only promotes the generation of a CO2-rich exhaust gas stream to enable carbon capture but also improves operating efficiency compared to conventional systems. The fuel cell system of the present invention circumvents known limitations (e.g., dilution effects) associated with conventional fuel cell systems configured to recirculate the anode exhaust gas stream.

[0020] One embodiment of this disclosure relates to a fuel cell system comprising a fuel cell module coupled to a fuel supply, an air supply, and a variable load. The fuel cell module may be configured to receive fuel from the fuel supply through a fuel inlet at a fuel electrode (e.g., anode) and to receive air from the air supply through an air inlet at an air electrode (e.g., cathode). The fuel cell system may further comprise an exhaust gas treatment module and / or a combustion assembly (e.g., an afterburner) fluidly coupled to an outlet of the fuel cell module. The exhaust gas treatment module may be configured to receive at least a portion of the fuel exhaust gas discharged from the outlet of the fuel cell module as a recirculation stream. The exhaust gas treatment module may be further configured to process the received fuel exhaust gas to enrich the fuel content within the recirculation stream before routing the recirculation stream back to the fuel inlet.

[0021] In various embodiments, the exhaust gas treatment module can be configured as a solid oxide electrolysis stack (SOEC) module. Therefore, the SOEC module can receive a portion of the fuel cell exhaust gas and enrich its fuel content therein through a co-electrolysis process, thereby reducing the net fuel supply requirements of the fuel cell system. In various embodiments, the SOEC module can be configured to utilize waste heat from the fuel cell to facilitate operation within the endothermic region, thereby improving the efficiency of the SOEC module.

[0022] The second embodiment involves using oxygen generated by electrolysis (e.g., oxygen produced by an SOEC module) as an oxidant for a combustion component (e.g., an afterburner). In various embodiments, using the electrolysis product as an oxidant allows for the combustion of exhaust products without the introduction of nitrogen (e.g., nitrogen from the air), resulting in a final outlet that is virtually a pure blend of CO2 and H2O. In various embodiments, H2O can be removed from the blend by condensation, leaving a high-purity CO2 stream for isolation or use in downstream processes.

[0023] refer to Figure 1The diagram illustrates a schematic representation of a conventional fuel cell system 10. The fuel cell system 10 can be a solid oxide fuel cell (SOFC) system with an SOFC module 15 fluidly coupled to an air supply 20 and a fuel supply 25, and thereby configured to generate power in electrical form. The SOFC module 15 can comprise a solid electrochemical cell containing a solid, impermeable electrolyte (e.g., dense ceramic) sandwiched between a porous anode (e.g., porous ceramic) and a porous cathode (e.g., porous ceramic). Oxygen supplied to the SOFC module 15 via the air supply 20 can be transported through the cathode to a cathode / electrolyte interface within the SOFC module 15, where the oxygen is reduced to oxygen ions. The oxygen ions can then migrate through the electrolyte within the SOFC module 15 to the anode. At the anode, the ionized oxygen can react with input fuel 30 received from the fuel supply 25 via an inlet manifold 35. In various embodiments, the fuel can be hydrocarbons, syngas, or any suitable fuel known in the art that releases electrons upon reaction with ionized oxygen. Power is generated when the electrons travel back to the cathode via external circuitry.

[0024] When ionized oxygen (i.e., ionized oxygen generated from the received air supply 20) reacts with input fuel 30, the SOFC module 15 can output oxygen via consumed air 40 and consumed fuel stream 45. As shown, consumed fuel stream 45 can be routed to output manifold 50, in which a first portion 55 of consumed fuel 45 can be sent to a fluidly coupled combustion assembly (“afterburner”) 60, and a second portion or recirculation stream 70 of consumed fuel 45 can form a recirculation stream returning to fuel inlet manifold 35. Afterburner 60 can also receive consumed air 40, and is configured to promote combustion of residual oxidant from consumed air 40 and the first portion 55 of consumed fuel 45 to produce a mixture of CO2 and nitrous oxide (NO). x The exhaust stream 65 contains nitrogen (N2) and H2O. When system 10 operates with excess air, the exhaust stream 65 may further contain oxygen (O2).

[0025] In various embodiments, SOFC module 15 may comprise a single SOFC cell. In other embodiments, SOFC module 15 may comprise multiple assembled fuel cells to form a fuel cell stack. In other embodiments, SOFC module 15 may comprise multiple fuel cell stacks. In various embodiments, SOFC module 15 may be configured to output electricity based on demand from one or more variable loads. In various embodiments, SOFC module 15 and / or coupling components within fuel cell system 10 may be communicatively coupled to one or more controllers to facilitate its operation.

[0026] Fuel cell system 10 includes a recirculation stream to recycle consumed fuel 45 back to SOFC module inlet 30. The fuel recirculation stream, such as fuel recirculation stream 70, can provide two advantages. In the case of hydrocarbon fuels, the product water in consumed fuel stream 45 can support steam reforming of fuel 25, thereby simplifying the overall system by eliminating the need for a separate water feed. Furthermore, fuel recirculation stream 70 can advantageously increase the total fuel content while disadvantageously reducing the fuel concentration at fuel input 30. It has been recognized in the prior art that excess fuel is typically required to achieve optimal overall system life and efficiency. Specifically, it should be recognized that operating an SOFC module, such as SOFC module 15, without an excess fuel supply from fuel supply 25 is impractical. For example, if SOFC module 15 were operated with only a stoichiometric fuel input from fuel supply 25, the result would be completely consumed outlet fuel (e.g., consumed fuel stream 45), which, while potentially beneficial for carbon capture, would destabilize SOFC module 15 and negatively impact its life and efficiency. Therefore, the amount of fuel required supplied by fuel supply 25 can typically exceed the amount of fuel involved in the electrochemical reaction within SOFC module 15 by at least 10%. Furthermore, since fuel cell system 10 generates an exhaust stream 65 containing various greenhouse gases and any unreacted fuel, this exhaust stream 65 must be output for downstream processing before being distributed for various applications or before the gases in the exhaust stream 65 are removed without contamination. This increased processing further reduces the efficiency of fuel cell system 10.

[0027] Figure 2 A schematic representation of a fuel cell system 100 according to an exemplary embodiment is shown. In various embodiments, elements 115 to 170 of the fuel cell system 100 are the same as or equivalent to corresponding elements 15-70 of the fuel cell system 10. Figure 2 As shown, the fuel cell system 100 may further include an exhaust treatment module 175, which is fluidly coupled to a second portion 170 of consumed fuel 145. In various embodiments, the exhaust treatment module 175 may be an SOEC module. The SOEC module 175 may include multiple branches electrically connected in parallel, wherein each branch includes at least one solid oxide electrolyzer stack, and wherein each solid oxide electrolyzer stack includes multiple solid oxide electrolyzers. In various embodiments, the SOEC module 175 includes an anode, an electrolyte layer, and a cathode, wherein the electrolyte layer is used to transfer ions between the anode and cathode to facilitate the generation of electrons for power generation.

[0028] As shown, SOEC module 175 can be positioned relative to SOFC module 115 such that waste heat 180 from SOFC module 115 can be used by SOEC module 175 to support its operation. SOEC module 175 can receive a second portion 170 of consumed fuel 145, which, in addition to containing various gaseous byproducts such as, but not limited to, CO2 and H2O, also contains remaining unreacted fuel from SOFC module 115. SOEC module 175 can cause the received second portion 170 to undergo and undergo a co-electrolysis process (i.e., electrolysis of both H2O and CO2) facilitated by waste heat 180, in which the gaseous byproducts can react to form fuel and oxygen. Therefore, SOEC module 175 can output a fuel-rich recirculated stream 185, which can then be routed to input manifold 135 for recirculation through SOFC module 115. Oxygen generated by SOEC module 175 can be removed from SOEC module 175 in outlet stream 190, which can be supplied as an oxidant to afterburner 160 to promote the combustion of unreacted fuel remaining in the first portion 155 of consumed fuel 145. As shown, implementing outlet stream 190 from SOEC module 175 as an oxidant for afterburner 160 allows for complete combustion of fuel in the first portion 155, resulting in the final exhaust stream 165 from afterburner consisting almost entirely of CO2 and H2O.

[0029] Because fuel cell system 100 regenerates fuel within SOEC module 175 to produce a enriched recycle stream 185 from a second portion 170 of consumed fuel 145 from SOFC module 115, fuel cell system 100 can (e.g., compared to fuel cell system 10) reduce the net fuel supply 125 required to operate fuel cell system 100. The efficiency loss attributable to the operation of SOEC module 175 can compensate for the efficiency gains due to the reduced inlet fuel demand 125, the use of waste heat 180, and / or the improved gas composition at inlet 130 (i.e., higher fuel content due to the enriched recycle stream 185), which can enable lower relative parasitics within fuel cell system 100 and / or a higher operating voltage for SOFC module 115 (e.g., compared to the operating voltage of fuel cell system 10).

[0030] In various embodiments, the SOEC module 175 can be configured as a separate module from the SOFC module 115 and can exchange heat with it via one or more gas streams. In other embodiments, the SOFC module 115 may include multiple stacks, each stack including multiple pools, wherein a portion of the pools within each stack may be an SOEC pool. In yet another embodiment, the SOFC module 115 and the SOEC module 175 may co-form multiple stacks, wherein the SOEC module 175 is housed within one of the multiple stacks.

[0031] In various embodiments, the SOEC module 175 can be configured to facilitate equipment and / or load balancing after operation of the fuel cell system 100 by assisting load absorption and / or power release. In various embodiments, the SOEC module 175 can be configured to facilitate the preservation of components of the fuel cell system 100 during a shutdown event. In various embodiments, the SOEC module 175 can be configured to act as a reducing gas source to protect the anode of the SOFC module 115. In various embodiments, the SOEC module 175 can be configured to introduce reducing gas during or immediately following a shutdown event.

[0032] In various embodiments, the fuel cell system 100 may be operatively coupled to one or more controllers configured to control the operation of the SOFC module 115, SOEC module 175, and / or other components contained within the fuel cell system 100. Therefore, in various embodiments, the fuel cell system 100 may be configured to monitor the composition of fuel gases input into the SOFC module 115 (e.g., input fuel 130) and / or the SOEC module 175 (e.g., via consumed fuel section 170). In various embodiments, the fuel cell system 100 may be configured to monitor the composition of fuel gases output from the SOFC module 115 (e.g., via consumed fuel 145) and / or the SOEC module 175 (e.g., enriched recycle stream 185). Therefore, the controllers may be configured to set and / or adjust one or more operating conditions of the fuel cell system 100 based on the monitored fuel gas composition within the system 100. In various embodiments, the fuel cell system 100 may be configured to implement a fuel gas composition that follows a protocol, wherein when it is determined (e.g., via a controller) that the fuel gas composition fails to meet one or more predetermined thresholds, the SOFC module 115 and / or SOEC module 175 may cooperatively or complementaryly adjust their operation to return the fuel gas composition (i.e., at the inlet and / or outlet within the system 100) to a satisfactory level. In various embodiments, the fuel cell system 100 may be configured to adjust the amount of fuel gas supplied by the fuel supply 125 based on fuel gas determination (e.g., via a controller).

[0033] In various embodiments, the fuel cell system 100 can operate under or near-operating conditions where the inlet fuel flow 125 can be set to approximately match the fuel electrochemically consumed in the SOFC module 115 (i.e., conditions known in the art of 100% fuel utilization). Therefore, when the inlet fuel flow 125 is controlled such that substantially all of the inlet fuel is electrochemically consumed in the SOFC module 115, the amount of unreacted fuel in the first portion 155 of the consumed fuel flow 145 can be determined primarily by the operating conditions of the SOEC module 175. For pure reactants (e.g., pure methane), such control may require scaling the inlet fuel flow 125 proportionally to the operating current. For fuels with different compositions (e.g., natural gas), the inlet fuel flow 125 can only be scaled directly to facilitate optimal CO2 capture if the composition and compositional measurements of the inlet fuel and / or exhaust are taken into account. Example compositional measurements may include characterization of the inlet fuel flow 125 or the exhaust (e.g., the consumed fuel flow 145, exhaust flow 165) using gas chromatography or similar analysis. Alternatively or alternatively, one or more oxygen sensors can be used to measure the oxygen concentration in the exhaust stream (e.g., via fuel-consuming stream 145, exhaust stream 165). Therefore, when the SOEC module 175 operates under stoichiometric conditions, the amount of oxygen in the outlet stream 190 can be approximately matched to the excess fuel in the first portion 155 of the fuel-consuming stream 145, such that, under substantially complete reaction conditions, the afterburner 160 can convert the remaining unreacted fuel into H2O and / or CO2. Thus, for example, by changing the ratio of fuel supplied from fuel supply 125 to the output of the SOFC module 115 to above and below 1.0, the stoichiometry in the afterburner 160 can correspondingly change from lean to rich, respectively. Unlike conventional systems, such as the fuel cell system 10 which always requires excess fuel from fuel supply 25, the fuel enrichment provided by the SOEC module 175 in the fuel cell system 200 enables stable operation when the inlet fuel from fuel supply 125 is at or below the level required to support the electrochemical power generation of the SOFC module 115.

[0034] In various embodiments, the fuel cell system may include one or more components to increase and / or regulate the flow rate of air and / or fuel gas therein. Figure 3A schematic representation of a conventional fuel cell system 200 is shown. The fuel cell system 200 may be an SOFC system with an SOFC module 215 fluidly coupled to an air supply 220 and a fuel supply 225, and configured to generate power to support a variable load 217. Heat generated by the SOFC module 215 can be discharged as waste heat 219. As shown, air from the air supply 220 can enter the fuel cell system 200 through an air inlet manifold 221 and circulate back to the SOFC module 215 via one or more blowers 224 fluidly coupled to the air inlet line 227. Similarly, fuel from the fuel supply 224 can enter the fuel cell system 200 through a fuel gas inlet manifold 235 and circulate back to the SOFC module 215 via one or more blowers 237 fluidly coupled to the fuel gas inlet line 230. As shown, oxygen consumed by the air can flow out of the SOFC module 215 via a consumed air stream 240. Similarly, fuel-consumed fuel gas can flow out of SOFC module 215 via fuel-consumed fuel gas stream 245. Fuel-consumed fuel gas stream 245 can be fluidly coupled to fuel output manifold 250, wherein fuel-consumed fuel gas stream 245 can be separated into a first consumed fuel stream 255 and a second consumed fuel stream 270. As shown, the first consumed fuel stream 255 and consumed air stream 240 can be routed together to afterburner 260, which is configured to combust residual fuel from the first consumed fuel stream 255 with oxygen from consumed air stream 240. In various embodiments, afterburner 260 can be fluidly coupled to one or more processing units 263, which can process combustion products and output the combustion products as exhaust stream 265 containing various gaseous byproducts and water.

[0035] like Figure 3 As shown, the second consumed fuel stream 270 can flow as a recirculated feed stream from the fuel outlet manifold 250 to the fuel inlet manifold 235, allowing the consumed fuel to be recirculated back to the SOFC module 215 via the fuel gas inlet line 230 through the blower 237. In various embodiments, in addition to products such as steam (H2O), the consumed fuel stream 270 can simultaneously supply additional fuel (at a lower concentration) to the SOFC module 215 to support steam reforming without requiring a separate water feed.

[0036] Therefore, fuel supply 225 must continue to supply a certain amount of fuel gas to fuel gas inlet line 230 to facilitate the operation of SOFC module 215. As shown, fuel cell system 200 may include a plurality of controllable valve assemblies 267 and 268 (e.g., solenoid valves, lift valves, etc.) disposed within each of air inlet line 227, fuel gas inlet line 230, consumed air stream 240, and corresponding first consumed fuel gas stream 255 and second consumed fuel gas stream 270. In various embodiments, fuel cell system 200 may include a plurality of release flow lines 269 fluidly coupled to air inlet line 227, fuel gas inlet line 230, and second consumed fuel gas stream 270 to facilitate pressure release therein (e.g., during a shutdown event). As described, exhaust stream 265 may contain a variety of gaseous byproducts, which may include, but are not limited to, CO2 and NO. x N2 and H2O.

[0037] In various embodiments, SOFC module 215 may comprise a single SOFC cell. In other embodiments, SOFC module 215 may comprise multiple assembled fuel cells to form a fuel cell stack. In various embodiments, SOFC module 215 and / or coupling components within fuel cell system 200 may be communicatively coupled to one or more controllers to facilitate its operation.

[0038] As previously described, in order to advantageously generate a combined final exhaust stream consisting primarily of CO2 and H2O, improve overall system efficiency, and reduce the amount of fuel required from the fuel supply, a fuel cell system may include one or more components for processing consumed air and / or fuel gases for recirculation and promoting carbon capture. Figure 4 A schematic representation of a fuel cell system 300 including an exhaust treatment module 375 according to an exemplary embodiment is shown. In various embodiments, the elements 215 to 270 of the fuel cell system 200 are the same as or equivalent to the corresponding elements 315 to 370 of the fuel cell system 300. Therefore, the fuel cell system 300 further includes an exhaust treatment module 375, which is fluidly coupled to both the second consumed fuel gas stream 370 and the fuel gas inlet manifold 335.

[0039] like Figure 4As shown, exhaust treatment module 375 is configured to receive consumed fuel gas from consumed fuel gas stream 370, which is discharged from SOFC module 315 via fuel gas outlet manifold 350 (e.g., anode exhaust). The consumed fuel gas received from consumed fuel gas stream 370 is fed into SOEC module 395. In various embodiments, exhaust treatment module 375 may be an SOEC module. SOEC module 395 may include multiple branches electrically connected in parallel, wherein each branch includes at least one solid oxide electrolyzer stack, and wherein each solid oxide electrolyzer stack includes multiple solid oxide electrolyzers. In various embodiments, SOEC module 395 includes an anode, an electrolyte layer, and a cathode, wherein the electrolyte layer is used to transfer ions between the anode and cathode to facilitate electron generation for power generation.

[0040] In various embodiments, the SOEC module 395 may be positioned relative to the SOFC module 315 such that waste heat from the SOFC module 315 can be used by the SOEC module 395 to support its operation. The SOEC module 395 may receive a second portion 370 of consumed fuel 345, which, in addition to containing various gaseous byproducts such as, but not limited to, CO2 and H2O, also contains remaining unreacted fuel from the SOFC module 315. The SOEC module 395 may cause the received second portion 370 to undergo and experience a co-electrolysis process (e.g., electrolysis of both H2O and CO2) promoted by waste heat, during which the gaseous byproducts may react to form fuel and oxygen. Therefore, the SOEC module 395 may output a fuel-rich stream 385, which may then be ultimately recycled through the SOFC module 315. Oxygen generated by SOEC module 395 can be removed from SOEC module 395 in outlet stream 390, which can be supplied as an oxidant to afterburner 360 to promote the combustion of unreacted fuel remaining in the first portion 355 of consumed fuel 345. As shown, implementing outlet stream 390 from SOEC module 395 as an oxidant for afterburner 360 allows for complete combustion of fuel in the first portion 355, resulting in final exhaust stream 365 from afterburner consisting almost entirely of CO2 and H2O.

[0041] like Figure 4As shown, the fuel cell system 300 may further include a water separation unit 403, which includes a condenser 410 fluidly coupled to a first manifold 400 and a second manifold 405. As shown, the water separation unit 403 may be configured to receive a enriched feed stream 385 output from the SOEC module 395. The enriched feed stream 385 may be received by the first manifold 400, which separates the feed stream such that a first portion 413 is separated and circulated to the condenser 410, where excess water can be removed from the first portion 413 of the enriched feed stream 385. This process not only improves the composition of the final recirculated feed stream but also acts as a cooling mechanism for a blower 337 configured to circulate fuel gas within a fuel inlet line 330 to the SOFC module 315. In various embodiments, the first portion 413 may constitute less than 20% of the total gas in the enriched feed stream 385. Once excess water has been removed from the first portion 413, it can be circulated to the second manifold 405 for recirculation as a recirculation stream 420 to the fuel gas inlet manifold 335. The second portion 415 of the enriched stream 385, including the remaining portion of the gas within the enriched stream 385, is directly circulated to the second manifold 405, where the gas in the second portion 415 can be mixed with the dried first portion 413 as it is recirculated to the fuel gas inlet manifold 335 via the recirculation stream 420. In various embodiments, a water separation unit 403 may be included within the fuel cell system 300 to prevent suppression of the stack voltage by supplying excess steam, which is caused by the implementation of the recirculation stream 420 coupled with a reduced inlet fuel flow (e.g., at SOEC module 395). Therefore, removing water from at least a portion of the enriched stream 385 leaving SOEC module 395 can promote SOEC module 395 stack maintenance efficiency. Similar to conventional systems such as fuel cell system 200, the recirculated feed stream (e.g., feed stream 370) of fuel cell system 300 can both increase the fuel at the gas inlet line 330 and provide products (e.g., primarily steam, H2O) that can support the reforming of the inlet fuel (e.g., at the gas inlet line 330), while also providing the water (e.g., in steam form) needed to support the steam reforming. However, unlike conventional systems (e.g., fuel cell system 200), the inlet fuel at the fuel gas inlet manifold 335 can be significantly reduced, and therefore less steam (H2O) is required for reforming and to prevent carbon deposition.

[0042] Because the fuel cell system 300 regenerates fuel within the SOEC module 395 to produce a enriched recycle stream 385 from a second portion 370 of consumed fuel 345 from the SOFC module 315, the fuel cell system 300 can (e.g., compared to the fuel cell system 200) reduce the net fuel supply 325 required to operate the fuel cell system 300. Furthermore, the efficiency loss attributable to the operation of the SOEC module 375 can compensate for the efficiency gains due to the use of waste heat and the improved gas composition at the inlet manifold 335 (i.e., higher fuel content due to the enriched and dry recycle stream 420), which can enable lower relative parasitics within the fuel cell system 300 and / or a higher operating voltage for the SOFC module 315 (e.g., compared to the operating voltage of the fuel cell system 200).

[0043] In various embodiments, the SOEC module 395 can be configured as a separate module from the SOFC module 315 and can exchange heat with it via one or more gas streams. In other embodiments, the SOFC module 315 may include multiple stacks, each stack including multiple pools, wherein a portion of the pools within each stack may be an SOEC pool. In yet another embodiment, the SOFC module 315 and the SOEC module 395 may co-form multiple stacks, wherein the SOEC module 395 is housed within one of the multiple stacks.

[0044] like Figure 4 As shown, the fuel cell system 300 may include a plurality of heat exchange components 427 and 428 (e.g., solenoid valves, lift valves, etc.) disposed within each of the air inlet line 327, the fuel gas inlet line 330, the consumed air flow 340, and the corresponding first consumed fuel gas flow 355 and second consumed fuel gas flow 370. In various embodiments, the fuel cell system 300 may include a plurality of thermally coupled paths 429 thermally coupled to the air inlet line 327, the fuel gas inlet line 330, and the second consumed fuel gas flow 370 to facilitate thermal management and thermal protection within the system 300.

[0045] In various embodiments, the SOEC module 395 can be configured to facilitate equipment and / or load balancing after operation of the fuel cell system 300 by absorbing auxiliary loads and / or releasing power. In various embodiments, the SOEC module 395 can be configured to facilitate the preservation of fuel cell system 300 components during shutdown events, as electrolyzer systems (such as the SOEC module 395) typically allow for rapid load switching, thereby safely absorbing relatively large power inputs. Typically, solid oxide electrolyzers (e.g., the SOEC module 395) tend to operate endothermally over a wide current density range. Therefore, the electrochemical efficiency of such systems may exceed 100% for most of their operating window, which may require external heat to sustain system operation. Thus, an SOEC module (e.g., the SOEC module 395) can typically operate at a higher reaction rate than an equivalent SOFC module (e.g., the SOFC module 315) before reaching its thermal limit, which is determined by the maximum heat that can be extracted from the SOFC module (e.g., the SOFC module 315) during steady-state operation. Therefore, the electrolytic rated power of an SOEC module (e.g., SOEC module 395) when it becomes thermally limited can be five times or more than the electrolytic rated power of an equivalent SOFC module (e.g., SOFC module 315). Consequently, from a control and stability perspective, the power level of an SOEC module (e.g., SOEC module 395) is typically more easily and rapidly changed than the power level of an equivalent SOFC module (e.g., SOFC module 315).

[0046] For example, a standard fuel cell, such as the SOFC module 315, can generate approximately 0.25 W / cm² during exothermic operation. 2 In contrast, electrolyzers such as the SOEC Module 395 can be configured to absorb approximately 1.3 W / cm³ when operating under near-thermal neutral conditions. 2 (That is, the power per unit active area of ​​the cell within the SOEC module 395) or more. Therefore, the integration of the SOEC 395 within the exhaust treatment module 375 allows the fuel cell system 300 to contribute to grid stability at a faster rate compared to conventional systems (e.g., fuel cell system 200). In various embodiments, the SOFC module 315 can operate based on time-averaged load conditions or demand, while the SOEC module 395 can provide high-speed modulation above or below average conditions (e.g., + / - 10%).

[0047] In various embodiments, SOEC module 395 can be configured to act as a reducing gas source to protect the anode of SOFC module 315. In various embodiments, SOEC module 395 can be configured to introduce reducing gas during or immediately after a shutdown event, or during a period of time during startup. In various embodiments, SOEC module 395 can be configured to control the generation of reducing gas in SOEC module 395 by monitoring the battery voltage in SOFC module 315, generating a voltage proportional to the fuel content (e.g., as defined by the Nernst equation) when SOFC module 315 is not generating power.

[0048] In various embodiments, the fuel cell system 300 may be operatively coupled to one or more controllers configured to control the operation of the SOFC module 315, SOEC module 395, and / or other components contained within the fuel cell system 300. Therefore, in various embodiments, the fuel cell system 300 may be configured to monitor the composition of fuel gases input into the SOFC module 315 (e.g., within the input fuel line 330) and / or the SOEC module 395 (e.g., via the consumed fuel flow section 370). In various embodiments, the fuel cell system 300 may be configured to monitor the composition of fuel gases output from the SOFC module 315 (e.g., via the consumed fuel gas flow 345) and / or the SOEC module 395 (e.g., the enriched feed flow 385 and / or the recirculated feed flow 420). Therefore, the controllers may be configured to set and / or adjust one or more operating conditions of the fuel cell system 300 based on the monitored fuel gas composition within the system 300. In various embodiments, the fuel cell system 300 may be configured to implement a fuel gas composition conforming to a protocol, wherein when it is determined (e.g., via a controller) that the fuel gas composition fails to meet one or more predetermined thresholds, the SOFC module 315 and / or SOEC module 395 may cooperatively or complementaryly adjust their operation to return the fuel gas composition (i.e., at the inlet and / or outlet within the system 300) to a satisfactory level. In various embodiments, the fuel cell system 300 may be configured to adjust the amount of fuel gas supplied by the fuel supply 325 based on fuel gas determination (e.g., via a controller).

[0049] In various embodiments, fuel cell system 300 can be configured to regulate the amount of fuel gas to the module and the amount of reforming on the stack in SOFC module 315 during transient events. In various embodiments, in order for fuel cell system 300 to follow load changes that might otherwise exceed the system response rate, fuel cell system 300 may release some CO2 into the environment during these transients. For example, if the fuel cell device must undergo rapid unloading, a conventional system (such as fuel cell system 200) may expose the SOFC stack (e.g., within SOFC module 215) to significant endothermic heat because unreformed fuel gas may partially or completely flow into the unloading stack before the fuel cell system has time to reduce the airflow at the stack. In contrast, fuel cell system 300 can be configured to rapidly increase the demand at SOFC module 395 to initiate a net device unloading process without unloading SOFC module 315. Therefore, when the fuel cell system 300 process control is regulated (e.g., via a controller) to reduce the supply of fuel gas (e.g., from supply 325), the SOEC 395 can follow the unloading profile of the SOFC module 315 while continuing to add hydrogen to the recirculation stream 420. If the power demand on the fuel cell system 300 increases rapidly, this addition of hydrogen to the recirculation stream 420, in addition to maintaining a fuel-rich environment, can also help maintain a reduced SOFC module 315 even during prolonged unloading events. In various embodiments, if the power demand increases rapidly, the power of the SOEC module 395 can be reduced while increasing the net power output of the fuel cell system 300 and reducing the load rate of the SOFC module 315.

[0050] Computational modeling data for a CO2-capturing fuel cell system 300, compared to a conventional fuel cell system 200, has demonstrated operational feasibility and shown improved performance due to the implementation of an SOEC module 395 and a water separation unit 303 within the exhaust gas treatment module 375. In summary, Table 1 below presents the relative performance parameters of the fuel cell system 300 compared to the conventional fuel cell system 200.

[0051] Table 1

[0052]

[0053] As understood in Table 1, the combination of SOEC module 395 and SOFC module can achieve a net increase in efficiency, while increasing the exhaust CO2 concentration in exhaust stream 365 from slightly above 5% dry to any close to 100% dry.

[0054] Furthermore, for a given net power output of the fuel cell system 300, which includes both the production of the SOFC module 315 and the consumption of the SOEC module 395, the fuel cell system 300 may require a larger SOFC module 315 (i.e., to facilitate a higher contribution from the SOFC module 315, such as 16% higher than the baseline). In various embodiments, the SOEC module 395 can be configured to operate at a higher current compared to a conventional fuel cell system (e.g., fuel cell system 200), which can reduce the net increase in the number of cells (or total cell active area) that must be included in the fuel cell system 300 to provide carbon capture functionality (e.g., an overall increase of 20% to 25%). In various embodiments, although the contribution of the SOFC module 315 increases by 14% and the cell size of the SOEC module 395 increases by 20-25%, the fuel supply of system 300 can be increased by approximately 3-5% compared to a conventional system (e.g., fuel cell system 200).

[0055] Furthermore, although competing methods exist for achieving carbon capture, fuel cell systems such as fuel cell system 300 offer superior operating characteristics. In summary, Table 2 below shows the operating parameters of fuel cell system 300 compared to baseline conventional systems (e.g., fuel cell system 200) and alternative competing systems for CO2 separation.

[0056] Table 2

[0057]

[0058] As understood in Table 2, the data were collected using computational modeling methods (i.e., HYSYS chemical process simulation) and supported by single-cell testing. With higher system fuel utilization and SOFC stack (within SOFC module 315) fuel utilization, the combination of SOEC module 395 and SOFC module 315 requires a higher total power output from SOFC module 315. Furthermore, fuel cell system 300 is comparablely capable of operating at higher efficiency and producing CO2 output with higher purity and only trace impurities (i.e., within exhaust stream 365). Moreover, compared to prior art oxygen-based competing systems, fuel cell system 300 requires a moderate increase in cell count (e.g., +20%) and a moderate increase in other process equipment (e.g., blowers, fuel blowers) while producing near-pure CO2 exhaust output, which can be easily redirected for downstream applications without additional treatment. Prior art oxygen-based competing systems result in lower overall efficiency and deliver exhaust CO2 with lower purity, limiting commercial applicability while also incurring higher capital costs and offering reduced operational flexibility. Furthermore, while competing amine-based CO2 capture technologies may be relatively well understood, these technologies present challenges due to high capital and operating costs. For example, the US DOE recommends that post-combustion carbon capture drives up electricity costs by 80% and results in a 20% to 30% efficiency loss. See the US Department of Energy website, page titled "Post-Combustion Carbon Capture Research," last accessed November 30, 2020, available at https: / / www.energy.gov- / fe / science-innovation / carbon-capture-and-storage-research / carbon-capture-rd / post-combustion-carbon. No competing carbon capture method offers the combination of high efficiency, relatively low capital costs, and high CO2 purity required for a fuel cell system.

[0059] Although the above text is Figure 1-4 The embodiments described herein are contemplated and considered within the scope of this disclosure, and various modifications and inclusions of these embodiments are envisioned.

[0060] It should also be understood that the construction and arrangement of the elements of the systems and methods shown in the representative embodiments are merely illustrative. Although only a few embodiments of this disclosure have been described in detail, those skilled in the art who examine this disclosure will readily understand that many modifications are possible (e.g., variations in the size, dimensions, structure, shape and proportions, parameter values, mounting arrangements, use of materials, color, orientation, etc.) without substantially departing from the novel teachings and advantages of the disclosed subject matter.

[0061] Therefore, all such modifications are intended to be included within the scope of this disclosure. Any device plus function clause is intended to cover the structure described herein as performing the stated functions, and not only a structural equivalent, but also an equivalent structure. Other substitutions, modifications, alterations, and omissions may be made in terms of the design, operating conditions, and arrangement of the preferred and other illustrative embodiments without departing from the scope of this disclosure or the appended claims.

[0062] Furthermore, the aforementioned functions and processes can be performed by dedicated equipment designed to execute specific functions and procedures. Functions can also be performed by general-purpose equipment that executes commands related to the function and procedure, or each function and procedure can be performed by equipment with different components, one of which serves as a control or separate control device.

[0063] The topics described herein sometimes demonstrate different components contained within or connected to different other components. It should be understood that the architectures thus depicted are merely exemplary, and many other architectures can actually be implemented to achieve the same functionality. Conceptually, any arrangement of components used to achieve the same functionality is effectively “associated” to enable the desired functionality. Therefore, any two components combined herein to achieve a particular function can be considered “associated” with each other to enable the desired functionality, regardless of the architecture or intermediate components. Similarly, any two such associated components can also be considered “operably connected” or “operably coupled” to each other to achieve the desired functionality, and any two components that can be so associated can also be considered “operably coupled” to each other to achieve the desired functionality. Specific examples of operational coupling include, but are not limited to, components that can be physically paired and / or physically interact and / or components that can wirelessly interact and / or logically interact and / or logically interactable components.

[0064] Regarding the use of virtually any plural and / or singular terms in this document, those skilled in the art can convert plural to singular and / or singular to plural as appropriate to the context and / or application. For clarity, various singular / plural permutations may be explicitly described herein.

[0065] Those skilled in the art will understand that, in general, the terms used herein, and especially in the appended claims (e.g., the body of the appended claims), are intended as “open-ended” terms (e.g., the term “including” should be understood as “including but not limited to,” the term “having” should be understood as “at least having,” etc., and the term “includes” should be understood as “including but not limited to,” etc.). Those skilled in the art will further understand that if a particular number of introduced claim statements are intended, then such intention will be explicitly stated in the claims, and in the absence of such statements, this intention is not presented. For example, to aid understanding, the appended claims may contain the introductory phrases “at least one” and “one or more” to introduce the claim statements. However, the use of these phrases should not be construed as implying that a claim statement introduced by the indefinite article "a" or "an" limits any particular claim containing such an introductory claim statement to an invention containing only one such statement, even when the same claim contains the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and / or "an" should generally be interpreted as meaning "at least one" or "one or more"); this is equally true for the use of definite articles used to introduce claim statements. Furthermore, even when a specific number of claim statements is explicitly stated, those skilled in the art will recognize that such statements should generally be interpreted as meaning at least the number stated (e.g., stating "two statements" without other modifiers generally means at least two statements, or two or more statements). Similarly, unless otherwise specified, the term "based on" should not be construed in a restrictive manner and should therefore be understood as "at least partially based on". Furthermore, in cases where idioms such as "at least one of A, B, and C" are used, generally, the intention of such a construction is that those skilled in the art will understand the idioms (e.g., "a system having at least one of A, B, and C" would include, but is not limited to, systems having only A, only B, only C, both A and B, both A and C, both B and C, and / or both A, B, and C, etc.). In cases where conventions such as "at least one of A, B, or C" are used, generally, such a construction is intended for those skilled in the art to understand the meaning of the convention (e.g., "a system having at least one of A, B, or C" would include, but is not limited to, systems having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.).Those skilled in the art will further understand that virtually any separate word and / or phrase presenting two or more alternative terms, whether in the specification, claims, or drawings, should be understood to account for the possibility of including one, any, or both of the terms. For example, the phrase "A or B" will be understood to include the possibility of including "A" or "B" or "A and B". Furthermore, unless otherwise stated, the use of words such as "approximately", "about", "around", "substantially", etc., implies plus or minus ten percent. Moreover, although the drawings show a specific order of method operations, the order of operations may differ from the order depicted. Furthermore, two or more operations may be performed simultaneously or partially simultaneously. Such variations will depend on the chosen software and hardware system and the designer's choices. All such variations are within the scope of this disclosure. Similarly, software implementations can be accomplished using standard programming techniques with rule-based logic and other logic for implementing various connection operations, processing operations, comparison operations, and decision operations.

Claims

1. A fuel cell system comprising: A fuel cell module having an inlet and an outlet, the fuel cell module being configured to receive a fuel flow comprising gaseous fuel at the inlet and discharge a consumed fuel flow at the outlet; An exhaust treatment module is fluidly connected to the fuel cell module and is configured as a solid oxide electrolysis stack module, the solid oxide electrolysis stack module including multiple solid oxide electrolysis cells. as well as An afterburner, the afterburner being configured to receive a first portion of the consumed fuel stream; The exhaust treatment module is positioned relative to the fuel cell module such that waste heat from the fuel cell module can be utilized by the exhaust treatment module. The fuel cell system is configured to direct a second portion of the consumed fuel stream to the exhaust treatment module, the consumed fuel stream comprising consumed fuel and at least one gaseous byproduct containing water and carbon dioxide; The exhaust treatment module is configured to use the waste heat from the fuel cell module to co-electrolyze the water and carbon dioxide in the second portion of the fuel-consuming stream to produce a fuel-rich stream and an outlet stream, the outlet stream including oxygen produced during the co-electrolysis in the second portion. The afterburner is configured to receive the outlet stream and use the oxygen in the outlet stream to burn the unreacted fuel in the first portion of the consumed fuel stream; and The fuel flow received at the inlet of the fuel cell module includes the fuel-rich feed stream and the inlet fuel stream; and The fuel cell system further includes a controller configured to control the inlet fuel flow such that the inlet fuel flow is approximately matched to the fuel consumed electrochemically in the fuel cell module.

2. The fuel cell system according to claim 1, wherein the waste heat facilitates the operation of the exhaust treatment module within the heat absorption region.

3. The fuel cell system according to claim 1, wherein the fuel cell module comprises at least one solid oxide fuel cell.

4. The fuel cell system according to any one of claims 1 to 3, wherein the exhaust treatment module comprises at least one solid oxide electrolyzer stack.

5. The fuel cell system according to claim 4, wherein the exhaust treatment module is housed within the fuel cell module.

6. The fuel cell system according to claim 5, wherein the fuel cell module comprises a plurality of fuel cell stacks.

7. The fuel cell system according to claim 4, wherein the exhaust treatment module is separate from the fuel cell module.

8. The fuel cell system of claim 2, wherein the controller is configured to operate the exhaust treatment module to provide reducing gas to the fuel cell module during a shutdown event of the fuel cell system.

9. A method of operating a fuel cell system, the method comprising: The fuel-consumed fuel stream is discharged from the outlet by the fuel cell module, which is configured to receive gaseous fuel at the inlet; The first portion of the consumed fuel stream is received by the afterburner, the first portion comprising consumed fuel and at least one gaseous byproduct containing carbon dioxide and water; The exhaust treatment module receives the second portion of the consumed fuel stream; The exhaust treatment module uses waste heat from the fuel cell module to co-electrolyze the steam and carbon dioxide in the first portion of the fuel-consuming stream to generate a fuel-rich feed stream and an oxygen-containing outlet feed stream. The afterburner uses oxygen from the outlet feed stream to burn the unreacted fuel in the first portion of the consumed fuel stream; as well as The fuel cell system directs the inlet fuel flow and the fuel-rich feed stream generated by the exhaust treatment module to the fuel cell module; as well as The exhaust treatment module is a solid oxide electrolysis stack module and includes multiple solid oxide electrolysis cells; and The inlet fuel flow is controlled by the controller of the fuel cell system such that the inlet fuel flow is approximately matched to the fuel consumed electrochemically in the fuel cell module.

10. The method of claim 9, further comprising: Water is removed from at least a portion of the fuel-rich feed stream by a water separation unit that is in fluid communication with the exhaust treatment module.

11. The method of claim 9, further comprising: The controller determines the amount of fuel consumed in the fuel cell module based on the composition of the consumed fuel stream.

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